the man who exposes his life to defend that of his friend, which he judges to be of more importance; neither of them act from humanity, or because they feel more exquisitely what concerns that other person than what concerns themselves.
 Adam Smith, The Theory of Moral Sentiments (1759). copy citation

Context

“We never are generous except when in some respect we prefer some other person to ourselves, and sacrifice some great and important interest of our own to an equal interest of a friend or of a superior. The man who gives up his pretensions to an office that was the great object of his ambition, because he imagines that the services of another are better entitled to it; the man who exposes his life to defend that of his friend, which he judges to be of more importance; neither of them act from humanity, or because they feel more exquisitely what concerns that other person than what concerns themselves. They both consider those opposite interests, not in the light in which they naturally appear to themselves, but in that in which they appear to others. To every bystander, the success or preservation of this other person may justly be more interesting than their own;” source